Pycnanthemum tenuifolium #1 (Narrow-leaved Mountain Mint)

Narrow-leaved Mountain Mint is an easy-to-grow, bushy, spreading wildflower native to dry, upland prairies and open woodlands over much of the eastern half of North America. It is a medium-sized, rhizomatous perennial that tends to colonize areas of low competition. It is not as aggressive as Mentha spp. and is easily kept in check by planting it with other competitive prairie species or surrounding it by hardscape in smaller gardens. It is great for larger rain garden areas, naturalizing in meadows, or for drawing in a plethora of pollinators that enthusiastically visit the flowers for nectar. It can be kept looking compact and tidy by cutting it back by half in late spring. The small, showy white flower clusters appear from late June to September and sit atop silvery-green, narrow foliage. The flower stalks are well-branched, resulting in a full, bushy effect.  It is believed that rubbing the fragrant, minty foliage over skin and clothing may repel pesky mosquitoes.

Sources:
Growing and Propagating Wildflowers by William Cullina
Herbaceous Perennial Plants by Allan M. Armitage
Missouri Botanical Garden
Lady Bird Johnson Wildflower Center
Illinois Wildflowers